Apparatus for combustion control of multiple furnace steam boiler



Oct. 6, 1964 H. D. MUMPER 3,151,601

- APPARATUS FOR couBusTIcm CONTROL OF HULTIPLE FURNACE swam BOILER 6A8 OUT Filed lay 18, 1961 3 Sheets-Sheet. l

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FUEL CONTROL 1 FUEL CONTROL L.. j 74 k 1.2. L I INVENTOR FLOW 'E HENRY o. MUMPER, DECEASED.

BY MARTHA A. MUMPERADMINISTRATRIX 3,151,601 APPARATUS FOR COMBUSTION CONTROL OF MULTIPL H. D. MUMPER Oct. 6, 1964 E FURNACE STEAM BOILER Filed lay 18, 1961 3 Sheets-Sheet 2 FIG. 2

INVENTOR HENRY D. MUMPER, DECEASED, BY MARTHA A. MUMPERADMINISTRATRIX Oct. 6, 1964 H. D. MUMPER 3,151,601

APPARATUS FOR comsusnou con-r1201. OF MULTIPLE FURNACE STEAM BDILER Flled May 18, 1961 s Sheets-Sheet a INVENTOR. HENRY D. MUMPER .DECEASED BY MARTHA A. BQUMPER, ADMINISTRATRIX United States Patent 3,151,661 APPARATUS FOR CGMBUSTION CONTRGL (1F MULTIPLE FURNACE STEAM BOILER Henry D. Mumper, deceased, late of Eatontown, Ni, by Martha A. Muinper, administratrin. Eatontown, Ni, assignor to Combustion Engineering, Inc., Windsor, Conn., a corporation of Delaware Filed May 18, 1961, Ser. No. 112,171 2 Claims. (Cl. 122-479) This invention relates to an improved technique for the control of fuel flow and air flow to a multiple furnace steam generator.

It is generally the designed intent in multiple furnace boilers in use today, to control the firing rate and the air flow such that these rates are approximately equal in the individual furnaces. When the heat absorbing surfaces perform according to design, the resulting temperatures of steam from the primary superheaters of two or more furnaces will be matched when the fuel and air flows to such furnaces are correctly matched. However, the control of fuel and air fiow generally is not practicable within a closer tolerance than plus or minus 5%, due to the difficulty in measuring large quantities with precision on an hourly or daily operating basis. The result of deviations in fuel and air flow in the above-mentioned range of plus or minus 5% can lead to unbalancing steam temperatures of the primary superheaters by as much as 40 to 60 F., thus endangering the life of the tubing and header materials of these superheaters due to overheating. It is particularly difficult to maintain even fuel flows in a coal fired furnace, where the moisture, weight and B.t.u. value of the fuel may vary considerably. Another problem encountered when using coal as the fuel is uneven slagging of the tubes making up the superheater sections in the furnaces. If uneven slagging does occur, the steam passing through the tubes of one of these sections will absorb considerably more heat from the gases, thus adding to the control problem, and further endangering such tubes.

It is an object of this invention to provide control means for the firing of a twin furnace boiler which will maintain the temperature of the steam leaving the primary superheater in each furnace substantially equal.

Other objects and advantages will become apparent from the following description of the illustrative embodiments, said embodiments being shown by the accompanying drawings wherein:

FIGURE 1 is a diagrammatic view, in the nature of a flow sheet, showing a twin furnace unit incorporating his invention;

FIGURE 2 is a modification of the control system shown in FEGURE 1;

FIGURE 3 is a schematic showing of a suitable pneumatic control arrangement that could be utilized in practicing the invention.

Looking now to FlGURE l of the drawings, 119 depicts the left hand furnace of a twin furnace unit. Mounted in furnace 16 is a burner unit 12. Pulverized coal is supplied to the burner 12 from bowl mill 14 by means of ipe 1s. Air to support combustion of the fuel is supplied to the burner 12 by means of duct 20 from forced draft fan 18.

The hot gases created by combustion of the fuel within furnace pass through a gas pass containing final superheater section 28, primary superheater section 24 and economizer 22. Water is heated in the economizer 22 which water is further heated in passing through tubes lining the walls of furnace 10 wherein part of the water is converted to steam. The water and steam mixture flows into the drum 6 where the water and steam is separated. The steam then flows from the drum into 3,151,601 Patented Get. 6, 1954 ice rimary superheater 24 where it is superheated. The superheated steam leaves superheater 24 by means of pi es 26 and passes on to final superheater section 28 where it is further superheated. Pipe 3% conveys the superheated steam from the final or high temperature superheater section 23 to its ultimate point of use, such as a steam turbine.

Fuel is also burned in the right hand furnace 49, which fuel is supplied to the burner 42 by means of bowl mill as and duct 46. Air to support combustion within furnace 4% is provided by means of forced draft fan 48 and duct 59. The gas pass of the right hand furnace 3-9 also contains an economizer 52, and a primary superheater 54. Steam also flows from the drum to primary superheater 54. The steam leaving primary superheater 54 flows by means of pipe se to final superheater section 28 located in the gas pass of the left hand furnace 10. The gas pass of the right hand furnace 411 also contains a reheater section 58. Steam enters the reheater section 5'8 from the high pressure section of the turbine by means of pipe at), and after picking up additional heat, flows back to the intermediate or low pressure section of the turbine by means of pipe 62.

The induced draft fans 64 and as, located downstream of the heat exchange members, keep the exhaust gases from the two furnaces flowing into stack 68.

As mentioned earlier, problems are encountered in trying to maintain the temperature of the steam leaving primary superheater sections 24 and 54 equal, to prevent overheating and burning out of the tubes within one or the other of these sections or the following sections 28 and 58. In accordance with his invention, the temperature of the steam leaving the primary superheater sections through tubes 26 and 55 is used to regulate the flow of air and fuel to each of the furnaces.

A signal 71) is received by the fuel flow bias control 72, which signal 71 represents the required combined total fuel flow to both furnaces 1i and 40. This signal 71) can come from any suitable sensing means, such as a steam pressure or steam flow measuring means within pipe 39, which conveys the steam from the furnace to the turbine. A signal 78 is received by air flow bias control 88, which signal 78 represents the required combined total air flow for both furnaces 11 and 40. A suitable means of determining the total air flow signal 78, would be a flow meter in pipe 30 to measure the steam flow therethrough, although other sensing means could be used equally as well.

A temperature sensing means such as a thermocouple, resistance thermometer, or a vapor temperature bulb is positioned within pipes 26 and 56. Signals representing these two temperatures are sent by means of 87 and 83 to a temperature difference controller 91 These signals 87 and 88 are amplified by controller and formed into a single impulse or signal 92 which impulse is transmitted both to the fuel flow bias control 72 and to the air flow bias control St and will determine the proportion of the total fuel flow and the total air flow which will go to furnace 19 and furnace 40 respectively. Such proportional signals from control 72, which are determined by signal 92, .pass on to left hand furnace fuel control 74 and right hand furnace fuel control 76 which will regullate the amount of fuel supplied to each furnace. Con trols 82 and 84 receive the proportional air flow control signals from controller 869 in like manner.

Member 86 represents a manual and/or automatic adjustment means, for varying the amount of air flowing to the left and right hand furnaces. One means would be an oxygen (0 controller. Such controller would have its sensing means positioned in the gas pass of each furnace downstream of the heat exchange members, and

would test the gases flowing through this portion of the gas pass to determine the oxygen content therein. If the oxygen content were too high or too low in either of the left hand or right hand gas passes, suitable adjustment'of the signal going either to control 82 or to control 84 would be made. For example, if the gases leaving furnace contain too high an oxygen content, 86 would send out a signal 85 which would tend to reduce the amount of air flowing to furnace 10. Likewise, if the oxygen content were too low, a signal would be sent out increasing the air flow to the furnace; The same holds true for the right hand furnace 40, as determined by the sensing means located in its gas pass.

Controls 72 and 80 can be any type of suitable pneumatic, hydraulic, or electrical control unit which is capable of adding or subtracting a plurality of received signals, thus forming one impulse or signal which varies in accordance with variations in the two or three received signals. a a

For example, control 80 could be comprised of two pneumatic relays such as illustrated in FIG. 1 of the Hagan Ratio Totalizer Bulletin 5452, published in 1952, one relay sending out a signal to control 82, and the other relay sending out a signal to control 84. Control 72 could likewise be made up of two pneumatic relays similar to control 80, the only difference being that control 72 will not receive a signal from control member 86, and thus the signals sent to 74 and 76 will vary in accordance to only two received signals, 70 and 92.

FIGURE 3 illustrates a suitable arrangement of the above.

The control illustrated in FIGURE 2 is the same as that shown in FIGURE 1, with the exception that the automatic adjustment control 86' sends its adjusting signal 85 to the fuel flow bias control 72 rather than to the air flow control 80'. With such a control the fuel rather than the air is adjusted in accordance with the si nals sent out from the sensing means located in the gas passes of the left and right hand furnaces.

With a control constructed in accordance with his invention, with the temperature of the steam leaving the primary superheater sections 24 and 54 being used to determine the amount of air and fuel flowing to each furnace, respectively, it is easy to maintain these two temperatures substantially equal. This eliminates any possibility of the tubes of one section from overheating to a point where they may possibly burn out or be damaged.

While the control has been'dscribed as being used to maintain the temperature of the steam leaving primary superheater sections 24 and 54 equal, it is obvious that it could also be used to maintain them at predetermined unequal temperatures. For example, it may be desired to have the temperature of one of the primary superheaters fifty or one hundred degrees higher than the temperature of the other. The disclosed control system would then be initially adjusted to maintain this temperature differential between the two.

While'he has illustrated and described the preferred embodiments of his novel control organization, it is to be understood that such is merely illustrative and not restrictive, and that variations and modifications may be made therein without departing from the spirit and scope of the invention. For example, while the control has been described in conjunction with a coal fired furnace, it may also be used on an oil or gas fired furnace. He therefore does not wish to be limited to the precise details set forth but desires to avail himself of such changes and alterations as fall within the purview of his invention.

What he claims is:

1. In combination, a multiple steam generator having two independent furnaces, each having its own fuel burner and its own fluid heating sections, first and second control means for controlling the amount of fuel and air being supplied to one furnace, respectively; third and fourth control means for controlling the amount of fuel and air being supplied to the other furnace, respectively; one of said furnaces having a first primary superheater therein, the other of said furnaces having a second primary superheater and a final superheater therein, the steam from both said first and second primary superheaters flowingto said final superheater, means responsive to a condition of the steam leaving said final superheater for determining the total amount of fuel and air required by said generator, temperature sensing means positioned in each of the primary superheater outlets which develop signals in accordance with the temperatures measured, fifth control means for comparing the two signals developed by the temperature sensing means, said fifth control means developing signals to he sent out to said first, second, third and fourth control means that proportions the fuel and air supplied to each furnace in such a manner that the temperature of the steam leaving each primary superheater is substantially equal, means responsive to conditions of the gases downstream of the fluid heating sections in one furnace for adjusting the signal to said first control means with respect to the signal to said second control means, and means responsive to conditions of the gases downstream of the fluid heating sections in the other furnace for adjusting the signal to said third control means with respect to the signal to said fourth control means, so that the amount of fuel and air supplied to each furnace results in optimum combustion efficiency of the fuel in each furnace.

2. In combination, a multiple steam generator having two independent furnaces, each having its own fuel burner and its own fluid heating sections, first and second control means for controlling the amount of fuel and air being supplied to one furnace, respectively; third and fourth control means for controlling the amount of fuel and air being supplied to the other furnace, respectively; one of said furnaces having a first primary superheater therein, the other of said furnaces having a second primary superheater and a final superheater therein, the steam from both said first and second primary superheaters flowing to said final superheater, means responsive to a condition of the steam leaving said final superheater for determining the total amount of fuel and air required by said generator, temperature sensing means positioned in each of the primary superheater outlets which develop signals in accordance with the temperatures measured, fifth control means for comparing the two signals developed by the temperature sensing means, said fifth control means developing signals to be sent out to said first, second, third and fourth control means that proportions the fuel and air supplied to each furnace in such a manner that the temperature of the steam leaving each primary superheater is substantially equal, means responsive to conditions of the gases downstream of the fluid heating sections in one furnace for adjusting the signal to said second control means with respect to the signal to said first control means, and means responsive to conditions of the gases downstream of the fluid heating sections in the other furnace for adjusting the signal to said fourth control means with respect to the signal to said third control means, so that the amount of fuel and air supplied to each furnace results in optimum combustion efficiency of the fuel in each furnace.

References Cited in the file of this patent UNITED STATES PATENTS 2,664,245 OConnor et al Dec. 29, 1953 2,784,912 Scutt Mar. 12, 1957 3,017,870 Profos Jan. 23, 1962 FOREIGN PATENTS 1,224,444 France Feb. 8, 1960 

1. IN COMBINATION, A MULTIPLE STEAM GENERATOR HAVING TWO INDEPENDENT FURNACES, EACH HAVING ITS OWN FUEL BURNER AND ITS OWN FLUID HEATING SECTIONS, FIRST AND SECOND CONTROL MEANS FOR CONTROLLING THE AMOUNT OF FUEL AND AIR BEING SUPPLIED TO ONE FURNACE, RESPECTIVELY; THIRD AND FOURTH CONTROL MEANS FOR CONTROLLING THE AMOUNT OF FUEL AND AIR BEING SUPPLIED TO THE OTHER FURNACE, RESPECTIVELY; ONE OF SAID FURNACES HAVING A FIRST PRIMARY SUPERHEATER THEREIN, THE OTHER OF SAID FURNACES HAVING A SECOND PRIMARY SUPERHEATER AND A FINAL SUPERHEATER THEREIN, THE STEAM FROM BOTH SAID FIRST AND SECOND PRIMARY SUPERHEATERS FLOWING TO SAID FINAL SUPERHEATER, MEANS RESPONSIVE TO A CONDITION OF THE STEAM LEAVING SAID FINAL SUPERHEATER FOR DETERMINING THE TOTAL AMOUNT OF FUEL AND AIR REQUIRED BY SAID GENERATOR, TEMPERATURE SENSING MEANS POSITIONED IN EACH OF THE PRIMARY SUPERHEATER OUTLETS WHICH DEVELOP SIGNALS IN ACCORDANCE WITH THE TEMPERATURES MEASURED, FIFTH CONTROL MEANS FOR COMPARING THE TWO SIGNALS DEVELOPED BY THE TEMPERATURE SENSING MEANS, SAID FIFTH CONTROL MEANS DEVELOPING 